This is one of three Macrosiagon species that Alice Abela and I saw during an end-of-July trip to the BugGuide gathering in southeast Arizona. Alice has posted images of this same individual here. The other two species we saw appear in the thumbnails below:



The species in the 2nd thumbnail above turned out to be Macrosiagon octomaculata...although in attempting to ID it, I initially keyed it to M. pectinatum. (By the way, M. pectinatum=M. pectinata...see "Nomenclatural Note" in remarks here).

In keying the individual in this post, I once again got M. pectinatum...but this time I believe I may have it right :-)

Here's the gist of the keying sequence for this specimen, as I interpreted it, using the keys in Rivnay(1) and Vaurie(2):

1) Metepisternum (=large pentagonal plate above middle leg) convex and bulging outward from the lateral suture with the pronotum above (vs. flat, not bulging from lateral suture above...as seen here);
2) Posterior central lobe of pronotum without semi-erect process (vs. with such a process, as seen here);
3) Pronotum without distinct lateral depressions or excavations (vs. with such excavations);
4) 2nd segment of hind tarsus shorter and thicker than 3rd, apices rounded (vs. 2nd and 3rd tarsomeres subequal);
5) Vertex rounded, front surface convex, pronotum black or (reddish) yellow but unicolorous.....pectinatum

Vaurie(3) states that while octomaculatum can have pronotum (reddish) yellow or blackish, that species never has a unicolorously black pronotum (i.e. there's always some red/yellow, for instance see here). On the other hand, the unicolorously black pronotum here is consistent with her comments regarding pectinatum.

The individual here also agrees well with the post below: